Hydrocracking catalysts and processes for their use are well known in the prior art. The literature on such catalysts and processes is quite extensive. Certain technical areas have been addressed as of particular interest as is readily apparent based on the large numbers of patents on certain technical topics, e.g., the use of certain zeolites as cracking catalysts. Representatives of the patents in this area are the ZSM patents which include: U.S. Pat. No. 3,894,934 (ZSM-5); U.S. Pat. No. 3,871,993 (ZSM-5, ZSM-11, ZSM-12 and ZSM-21); U.S. Pat. No. 3,702,886 (ZSM-5); and U.S. Pat. No. 3,758,403 (ZSM-5 in combination with zeolite Y) of and U.S. Pat. No. 3,972,983 (ZSM-20).
Although the aforementioned patents on the use of ZSM-type zeolites in hydrocracking catalysts are of interest, the use of these zeolites has not been of significant commercial interest to date. The commercially significant activity in the hydrocracking area has been for the most part directed to further elaboration on the basic hydrocracking technology which has arisen in relation to zeolite Y, as disclosed in U.S. Pat. No. 3,130,007.
The development of hydrocracking catalysts based on a Y-type zeolite has taken many directions. Illustrative of the various processes which have arisen are those disclosed in the following patents:
U.S. Pat. No. 3,293,192 discloses a "synthetic ultra stable zeolitic aluminosilicate: of the Y-type" (see: U.S. Pat. No. 3,594,331 which discloses that Z-14HS is zeolite Y) which has been prepared by calcining a low alkali metal Y zeolite and successively base exchanging the calcined product with a base solution containing ammonium or complex amino salts until the alkali content is less than 1 weight percent and then calcining this product.
U.S. Pat. No. 3,493,519 discloses a process for calcining an ammonium-Y zeolite in the presence of rapidly-flowing steam followed by base exchange and treatment of the product with a chelating agent capable of combining with aluminum whereby aluminum is extracted from zeolite Y.
U.S. Pat. No. 3,506,400 discloses an improved process for extracting aluminum from a zeolite similar to that disclosed in U.S. Pat. No. 3,493,519. The improvement is to employ mineral acids in the aluminum extraction process.
U.S. Pat. No. 3,513,108 discloses a process for improving the hydrothermal stability of aluminosilicates by subjecting the hydrogen form of the aluminosilicate to calcination in an inert atmosphere with the resulting water, generated as a result of the calcination, being allowed to react with the resultant crystalline aluminosilicate.
U.S. Pat. No. 3,594,331 discloses a process for treating a crystalline aluminosilicate by treating the zeolite with a soluble fluoride salt. The process is disclosed to be a stabilization process wherein fluoride becomes associated with structural Na.sub.2 O.
U.S. Pat. No. 3,640,681 discloses a process for extracting aluminum from the framework of a crystalline zeolitic molecular sieve by use of acetylacetone and a metal acetylacetonate as extractants.
U.S. Pat. No. 3,691,099 discloses a process for extracting aluminum from a crystalline zeolitic aluminosilicate by use of an acidic solution containing at least one water soluble salt which reacts with aluminum atoms of the zeolite.
U.S. Pat. No. 3,933,983 discloses a process similar to the process of U.S. Pat. No. 3,594,331 except that a cation exchange step is added after the fluoride treatment step.
U.S. Pat. No. 4,093,560 discloses a process for dealuminizing, i.e., extracting aluminum therefrom by treatment with an acidic slurry of an ammonium or alkali metal salt which upon acidification complexes aluminum. The aluminum removal process destroys at least a portion of the crystallinity of the support material.
U.S. Pat. No. 4,242,237 discloses a catalyst comprising a mixture of a Y-type zeolite and a small pore zeolite, e.g. zeolite A.
The above patents are illustrative of the state of the hydrocracking art. Although there has been extensive development of Y-type hydrocracking catalysts there has been little development of truly new hydrocracking catalysts. This paradox, the lack of new catalytic materials despite the sizable economic interest, is readily understood by an appreciation of the fact that the work horse of the commercial hydrocracking business is zeolite Y. As a result, the patent literature discloses the clear preference towards improving zeolite Y.
The existence of zeolite Y and its use as a catalyst for hydrocracking processes is now well accepted if not, in fact, legendary. Still, the state of the art relating to zeolite Y and its use in hydrocracking catalysts has been generally limited to ion-exchange techniques, aluminum extraction techniques and other secondary treatment processes which tend to remove aluminum from zeolite Y. Such aluminum deficient products necessarily contain significant levels of defect structure (hereinafter defined) as a result of the extraction of aluminum and as a result should have the common deficiencies observed in such materials, including reduced chemical and thermal stabilities which ultimately result in reduced catalyst life. What is missing in the prior art is a new form of zeolite Y wherein zeolite Y, has in fact been modified in a way other than by only extracting aluminum to lower the aluminum content with the resulting increase in the concentration of defects in the crystal structure. Such a composition would be unique in its structure and in its utility as a hydrocracking catalyst.
One such method for producing such a material is disclosed in U.S. Ser. No. 315,853 filed Oct. 28, 1981, commonly assigned, wherein zeolite Y (as well as may other zeolites) may be contacted with a fluorosilicate salt in an amount of at least 0.0075 moles per 100 grams of the zeolite Y (on an anhydrous basis) and where said fluorosilicate salt is provided in the form of an aqueous solution having a ph value within the range of 3 to about 7. The aqueous solution of the fluorosilicate salt is brought into contact with zeolite Y at a rate sufficiently slow to preserve at least 80 percent, preferably at least 90 percent of the crystallinity of the starting zeolite Y and silicon atoms, as SiO.sub.4 tetrahedra, are inserted into the crystal lattice in substitution for aluminum atoms. The final material is truly the first material known to have been prepared wherein the molar ratio of SiO.sub.2 to Al.sub.2 O.sub.3 was changed by a concurrent aluminum extraction and SiO.sub.2 insertion. The uniqueness of this product is readily apparent from a consideration of the fact that in over seventeen (17) years since the publication of zeolite Y that only the materials of U.S. Ser. No. 315,853 have been prepared to have SiO.sub.2 /Al.sub.2 O.sub.3 ratios greater than 6 while not containing the significant defect structure which is necessarily associated with any process which extracts aluminum from the framework..sup.* FNT .sup.* There has been one report (G.B. No. 1,431,944) of the preparation of a faujasite-type structure (Zeolite 529) having a high silica to alumina ratio. The patent alleges that a direct synthesis process prepared a faujasite zeolite having a silica to alumina ratio between 5.5 to 8.0 (see claim 11). Unfortunately, the patentees failed to prepare such materials and reported silica to alumina ratios based on measurements employing dehydrated samples. Apparently, the patentees did not appreciate the fact that during the preparation of Zeolite 529 that the heating step at 110.degree. C. or greater dehydrated the prepared materials which resulted in an erroneously low a.sub.o and, therefore, an erroneously high SiO.sub.2 /Al.sub.2 O.sub.3 ratio based on the a.sub.o. The net result appears to be simple, i.e., Zeolite 529 is simply a form of zeolite Y.